1. Field of the Invention
The present invention relates to an image processing apparatus, an inkjet printing apparatus and an image processing method, and more particularly, to a technique for suppressing degradation in image quality caused by a bronzing phenomenon observed on a printed image.
2. Description of the Related Art
In inkjet printing, particularly distinguishing phenomena occurring in use of pigment ink for a glossy print medium includes a phenomenon in which an illumination image reflected on the surface of a printed material takes a color (hereinafter referred to as a “bronzing phenomenon”). For example, in the use of a cyan pigment, the illumination image becomes reddish, which contributes to a significant loss in visual image quality. A known method for lessening such a bronzing phenomenon is lamination of a clear film onto the print surface to prevent pigment particles from being exposed at the surface of a print medium. However, having the lamination construction gives rise to disadvantages of increased device costs, increased time required for the lamination process, and the like.
To address it, Japanese Patent Laid-Open No. 2001-138555 discloses a technique for controlling a ratio of used ink to lessen the bronzing phenomenon. The technique is the method where the presence or absence of occurrence of the bronzing phenomenon is determined from the lightness of an input image and a ratio of used ink, and then the ratio of ink to be used is changed based on the determination result, thus lessening the bronzing phenomenon.
In general, when viewing a printed material, the viewer views light reflected off the printed material upon which light is incident from a light source. Then, such a viewed color varies by a viewing angle. FIG. 1 is a diagram illustrating difference between two reflected lights when a viewer views a printed material at two different angles. In FIG. 1, the reflected light viewed in direction A is specular reflected light viewed in a specular direction with respect to the light source, in which a light source image reflected on the printed material is viewed. On the other hand, the reflected light viewed in direction B is light reflected after passing through the interior of the printed material, that is, diffused light, in which color reproduced by color materials (hereinafter referred to as “print color”) is viewed.
In the viewing in the direction A of such two viewing angles, a different color reflection of the light source from the original color of the light source may be possibly recognized, which is perceived as the bronzing phenomenon. In addition to the event of such a reflection of the light source, the two types of the reflected lights as shown in FIG. 1 may be simultaneously viewed. As a result, for example, an image of a different color from the original print color may possibly be seen. This is also recognized as the bronzing phenomenon.
If the original print color differs from the color produced by the bronzing phenomenon (hereinafter referred to as a “bronzing color”) as described above, such a bronzing color is perceived as an undesired color, resulting in degraded image quality of the printed material. To address it, in Japanese Patent Laid-Open No. 2001-138555, the ratio of ink used is changed to lessen the bronzing phenomenon as described earlier. However, degradation in image quality caused by a difference between the bronzing color and the print color cannot be adequately controlled. That is, even when the bronzing color or the developed color is processed to become indistinct, if the difference of the bronze color from the print color is large, the large difference itself is noticeably recognized, becoming a factor that degrades the image quality.